The invention relates to formulations and methods for straightening or relaxing the curl of hair, particularly naturally kinky and curly hair.
Hair generally can be divided into four categories: (i) straight, (ii) wavy, (iii) curly, and (iv) kinky. The human hair shaft is comprised of three concentric layers identified as the cuticle (a thin, outer-most shell); the cortex (the main body of the hair); and the medulla (a thin, central core). The cuticle and cortex are responsible for the hair shaft""s mechanical properties, that is, its tendency to curl (in some hair the medulla is absent). The condition of the cuticle is responsible for the outward appearance of the hair, particularly feel and shine. Straight hair resembles a rod with a circular diameter; wavy hair shafts are compressed into an oval diameter; curly shafts are further compressed into an elongated ellipse; and kinky hair shafts are flatter still. Hair shaft configurations can be represented as follows: 
Many people with naturally kinky, curly, or even wavy hair often desire to straighten their hair. There are a number of hair straightening compositions and methods available today, but these involve use of harsh straightening agents such as alkaline or sulfite-based chemicals. To permanently alter the natural curl of human hair, a number of types of bonds within the hair are cleaved, including salt bridges and disulfide bonds. Human hair is composed of cross-linked, xcex1-helix protein, primarily keratin. Keratin is a complex of polypeptide chains of high molecular weight. The hair shaft will maintain its outward shape by ionic bonding or salt bridges (disulfide or cystine bridges) which pair various amino acids found in the hair. Current straightening methods break disulfide bonds into free sulfhydryls and then re-establish new disulfide bonds in the desired configuration by reduction/oxidation of the hair shaft using various chemicals.
Most permanent straightening products marketed today use one of five types of chemicals: (1) thioglycolate-based products, (2) sulfite-bisulfite products, (3) sodium hydroxide (alkali) products, (4) lithium hydroxide, and (5) acetamide (formulated as a between-shampoos, aerosol styling aid). See, e.g. AMA BOOK OF SKIN AND HAIR CARE, Schoen, LA, Ed., American Medical Association, (JB Lippincott Co., New York 1976), which is incorporated herein, at p. 116-119. In all these cases excepting acetamide, the chemical agent is applied to clean, damp hair that has been pulled straight by combing action. After a carefully-measured period of time, the disulfide bonds are broken, the solution is rinsed off, and a second solution (often hydrogen peroxide or other oxidizing agent) is applied to neutralize the reaction. These products produce varying levels of effectiveness in hair straightening; however, there are drawbacks to using them in terms of safety, toxicity, risk of damaging the hair, and protection of the skin and scalp.
For example, thioglycolate straighteners produce reversible changes in the chemical disulfide bonds of hair by generating free oxygen radicals for 10 to 20 minutes. Concern about the teratogenicity of thioglycolate has recently caused the United States Department of Health and Human Services to post notice of a need to review their safety for human use. Bisulfite straighteners produce reversible bond changes, and are milder on skin than thioglycolate straighteners. However, bisulfite straighteners still present a risk of hair and skin damage, and they are typically used in combination with alkaline agents which can irritate and burn the skin and scalp. In the straightening procedure, bisulfite lotion is applied to clean, damp hair, which is covered in plastic for a period of time, then combed straight, rinsed, treated with an alkaline stabilizer, and conditioned.
Like other known methods, alkali lotions cannot be used on irritated or injured scalps. Also, the harshness of alkali lotions presents the risk of skin irritations or burns on a healthy scalp. As new hair grows in, it alone should be exposed to the chemical straighteners, an often delicate and difficult procedure that avoids lotion contact with both the scalp and the previously treated hair. In this method, sodium hydroxide lotion is applied to the hair and smoothed flat with finger pressure. A xe2x80x98normalizerxe2x80x99 pre-shampoo rinse is then applied followed by a water rinse. The hair is then shampooed twice, conditioned and administered a setting/styling/wrapping lotion prior to styling and drying.
Typically, to be effective as a straightening agent, the alkali hair straighteners include use of about 1.8 to 4 weight % of strong bases, such as sodium hydroxide, potassium hydroxide, or lithium hydroxide. Use of alkali agents at these concentrations result in compositions having pH values of above 9pH, and more often above 12 pH. For example, a hair relaxer referred to as CLEARGEL 862(trademark) uses a 50% solution with 3.5 wt. % sodium hydroxide which produces a composition having a pH of 12.5 to 12.7 at 25xc2x0 C. Use of alkaline agents at such concentrations presents a safety risk and also complicates the process of hair straightening, as various steps need to be made to protect the scalp and administer the lotion. As an illustration, U.S. Pat. No. 4,592,908 to Wajaroff et al. discloses a protective cream that is adapted to be applied to the scalp before a strongly alkaline hair-straightening agent is used. Wajaroff""s cream comprises VASELINE(copyright) and organic acids, containing less than 1% water, which is applied to the scalp, but not the hair. A strongly alkaline hair-straightening agent is then applied to the hair. According to the Wajaroff method, the cream placed on the scalp will neutralize the alkaline agents that may reach the scalp, thus protecting the scalp. The Wajaroff method, however, uses strongly alkaline agents, and additionally, it requires extra steps in applying the protective gel to the scalp and then removing that gel after the hair straightening steps have been performed.
The xe2x80x9cno lyexe2x80x9d method uses lithium hydroxide, also a human toxin, in combination with other ingredients as the relaxing agent. The user is also cautioned against skin and scalp bums, possible hair loss, and eye injury. The product is contraindicated for persons with damaged or chemically-treated hair and irritated scalp. Acetamide (CH3CONH2) is an organic, crystal compound in the urea and guanine series which has recently been formulated into a cosmetic spray-on, straightener styling aid for use between shampoos.
Acetamide is a known irritant to the eyes, nose, and throat and has shown low-to-moderate acute toxicity from oral exposure, including liver tumors, in animal studies.
Other methods of breaking disulfide bonds in hair employ high-heat appliances. In this method heat combs set at 300xc2x0 F. are pulled quickly through long hair, which instantly breaks disulfide bonds leaving the hair straight. This process can result in damaging hair permanently if the temperature and combing speed are not carefully managed.
U.S. Pat. No. 3,654,936 to Wajaroff describes the use of a keratin softener for straightening hair. In this method hair is treated with a reducing agent then straightened by the action of a xe2x80x9ckeratin softenerxe2x80x9d combined with swelling or penetration-promoting agents, while being straightened mechanically prior to the application of a fixation agent.
Other straightening methods include the use of humectants such as fatty acid lactylates and fatty acid glycolates to improve the hair""s texture (see U.S. Pat. No. 4,424,820, xe2x80x9cHair Straightening Compositions Containing Fatty Acid Lactylates and Glycolates and their Method of Use,xe2x80x9d issued to Cannell, D. et al. and assigned to Redken Laboratories, which is incorporated herein), and the use of dipropylene glycol monomethyl ether as a swelling and penetrating agent. (See U.S. Pat. No. 4,859,459, xe2x80x9cMethod of Shaping Human Hair Using Dipropylene Glycol Monomethyl Ether,xe2x80x9d Greiche, J., et al., assigned to Wella Aktiengesellschaft, Germany, also incorporated herein.)
Accordingly, the current methods of hair straightening remain dangerous to the skin, eyes, and hair. In some cases, direct contact between the skin and the straightening agent can result in second- and third-degree chemical burns or even hair loss. None of the known methods are recommended if the scalp or skin is sensitive, scaly, scratched, sore or tender. Unsatisfactory and sometimes harmful results occur if the directions are not carefully followed. As may be appreciated, there is a need for a hair-straightening composition and method that avoids the use of harmful chemicals and irritants that have been used in previous compositions. There further remains a need for a hair straightening agent that provides the consumer with a greater choice of options and products that may be safely used at home.
Applicant has discovered a formulation for straightening hair that avoids the dangers of the alkaline and other harsh ingredients of prior art compositions. The present invention relates to formulations for straightening hair comprising alkanoic acids, combined with water, optionally in combination with other suitable diluents. The inventive formulation is acidic, not alkaline, and the acids suitable for use in the inventive formulations preferably are selected from acetic and propanoic acids. The invention does not use an alkaline hair-straightening agent to perform the hair straightening function. Instead, the step of hair straightening is accomplished by applying the non-alkaline, alkanoic acid and water formulation to the hair and then either leaving the formulation in the hair without rinsing, or shampooing the formulation out of the hair followed by optional conditioning. The formulation is also effective for hair-straightening maintenance, relaxation of curl, and reduction of frizziness of hair produced from humid weather.